This application claims the benefit of a priority under 35 USC 119(a)-(d) to French Patent Application No. 02 06443 filed May 27, 2002, the entire contents of which are hereby incorporated by reference.
This invention relates to a double resonance electronic converter and a method operating such a converter, which may be used to obtain very high dc voltages, on the order of 100 kilovolts and more, for providing power, e.g., to an X-ray tube in a radiological imaging apparatus.
There exist many types of electronic converters including the type known as the xe2x80x9cdouble resonancexe2x80x9d. The xe2x80x9cdouble resonancexe2x80x9d uses a circuit having two resonance frequencies.
A double resonance electronic converter generally comprises four parts: a switching circuit; a double resonance circuit; a rectifying and filtering circuit; and a control circuit for the switching circuit. The switching circuit comprises two switches whose switching on (conduction) or off (break) are controlled by the control circuit. A dc voltage is applied to the terminals switches so that the potential of the positive pole is applied to the resonance circuit when only one switch is on, while the potential of the negative pole is applied when only the other switch is on.
The resonance circuit comprises: a parallel resonant circuit comprising an inductor and a capacitor; a series resonant circuit comprising inductors, as well as a capacitor; and a transformer.
The rectifying and filtering circuit comprises two rectifier diodes, two filtering capacitors and a load resistor. The output voltage of the converter is taken from the terminals of resistor.
The control circuit controls the conduction and blockage of the switches as a function the following three parameters: the series current in one inductor; the parallel current in another inductor; and the measured output voltage.
The operating characteristics of the resonant circuit provides a curve of the modulus of the frequency response between an input voltage at the common node of the switches, and an output voltage at the terminals of capacitor. This curve shows two resonance frequencies and zero transmission at an intermediate frequency. The conduction of one of the switches establishes a direct current in the resonant circuit that unbalances the series current and deactivates the parallel current.
The invention and embodiments thereof is a method and circuit for controlling the switches of a double resonance converter so as to obtain a balanced start up condition.
In an embodiment of the invention the start of the conduction of the switches is synchronized with the value of the parallel current. More particularly, the start of the first conduction of one of the switches is carried out at the maximum positive value of the parallel current.